The invention relates to the continuous casting of metals and in particular of steel.
More specifically, the invention relates to a supply and control method for depositing on the surface of the metal bath in a continuous casting mold, an evenly distributed layer, of predetermined thickness, of a powdery or granulated material, said method being of the type wherein the surface of the metal bath is supplied by gravity with said material by way of a supply conduit whose end portion is provided with a delivery nozzle situated above the surface of said metal bath.
The invention also relates to the device used for carrying out said method.
During continuous casting, the steel bath inside the mold is permanently covered with a layer of powdery or granulated material, designated hereinafter as the powder. The object of this powder is to heat-insulate the bath, to prevent the metal from re-oxidizing, to absorb floating inclusions, and finally to lubricate the walls of the mold. The powder is liquefied into slag when in contact with the liquid metal and the walls of the mold become coated with said slag when said mold oscillates upwardly. Each oscillating movement therefore means a reduction in the quantity of slag on the metal bath, this resulting in a reduction of the thickness of the layer of powder. The powder supplied to compensate for the powder consumed varies in relation to the characteristics of that powder, to those of the casting machine, to the working conditions of said machine as well as to the characteristics of the cast metal. The four functions of the powder are, in practice, optimized by keeping a constant thickness of the layer covering the metal bath. The height of said layer can be adjusted by hand or automatically. An automatic method has been found to ensure a more reliable operation, safer working conditions, a better quality of the molded products, and a reduction in staff costs.
Automatic installations are already known, from French Pat. Nos. 2 231 456 and 2 432 353, for spreading out powder and controlling the thickness of the formed layer, in which the supply of powder designed to compensate for the powder consumption is initiated by a detection of absence of powder or reduction of the thickness of the powder layer. Sensors with associated electric and electronic equipments are used to this effect, these equipments processing the signals of the sensors and controlling, by delayed action, mechanized quantity-measuring and supplying devices to restore the predetermined thickness of the powder. Automatic installations of this type have the disadvantage however of not keeping a constant thickness of powder. The preset and irregular compensations indeed lead to repeated overconsumptions or shortages of powder. Their reliability is doubtful due to a multiplication of the risks of failure in the relatively sophisticated equipments which have to be used. Another disadvantage is their high purchase and operating costs.